The term “Built-in Self-Test” or “BIST” refers to systems and techniques used by a machine or device to test itself. Generally speaking, a goal of a BIST mechanism is to reduce a manufacturer's use of external test equipment in order to determine whether a device works properly. In some cases, a BIST mechanism may also give the manufacturer the ability to test portions of a device that are not otherwise accessible from its exterior. In this context, a “Logic BIST” or “LBIST” is a form of BIST in which hardware and/or software is built into an Integrated Circuit or “IC”, thus enabling the IC to test its own operation without relying upon other devices.
To test one or more portions of an IC (referred to as a “Circuit Under Test” or “CUT”), an LBIST controller may introduce a pattern of values into a scan chain (a series of flip-flops or latches) within a given portion during a shifting operation, and then it may observe the results of the propagation during a capture operation. If the captured results reveal an expected “signature,” the CUT is determined to be operating properly. Otherwise, the CUT may be deemed defective and corrective action may be taken.
To perform some of these operations, an LBIST controller may access certain points internal to the CUT in order to inject portions of the test pattern at those points; which are also known as “test control points.” Additionally or alternatively, the LBIST controller may set inputs to the CUT within the IC to predetermined, known values, in a process referred to as “x-bounding.” Traditionally, each test control and x-bounding point has included its own dedicated flip-flop, latch, register, and/or multiplexer.